1. Field of the Invention
The present invention relates to systems for controlling the operation of an appliance and the like and is more particularly disclosed as it would be adapted to control a drying apparatus such as a clothes dryer, washer-dryer, etc.
Generally speaking, the control system of the present invention includes a control element for processing a plurality of signals representing programmable values of operation variables and representing varying conditions associated with the operation of an appliance in accordance with a control strategy, first means for addressing the control element with signals representing desired values of the operation variables, second means for addressing the control element with the signals representing varying conditions associated with the appliance operation, the second means for addressing the control element including at least two sensors for sensing the varying conditions, and means responsive to the control element for activating and deactivating at least one machine function of the appliance in accordance with the control strategy.
Furthermore, a method of controlling the operation of the appliance includes a step of deriving a final value difference between varying conditions indicative of desired results. This final value difference is a function of a maximum value difference between varying conditions and a predetermined result to be achieved by operation of the appliance.
2. Description of the Prior Art
In a typical drying apparatus such as a clothes dryer, it is generally desirable to be able to at least control the dryness of the articles being dried at the conclusion of an operation cycle. Furthermore, it may be desirable to control the temperature of the air used during the drying operation, the temperature of the air after the articles have been dried to a desired degree of dryness, or the operation of the apparatus in response to the existence of a condition which if left undetected could cause damage to the apparatus or result in its inefficient operation.
Various control systems have been devised to control at least one of the aforementioned operation variables of a drying apparatus. In general, these conventional control systems have been directed to the control of the dryness of the articles being dried at the conclusion of an operation cycle of the drying apparatus (See U.S. Pat. Nos. 3,333,345; 3,809,924; and 3,822,482) and have typically employed sensors for sensing the moisture content of the articles. Accordingly, the conventional control systems have been limited in the number of operation variables they are capable of controlling without the addition of sensors and associated control circuitry. Furthermore, these conventional control systems are incapable of economically providing the user of the drying apparatus with the option of either timing an operational cycle of the apparatus or controlling it independent of time by dryness sensing.
In U.S. Pat. No. 3,333,345 there is described a dryness control system which includes a single sensor that controls the operation of the dryer in accordance with the dampness of the articles being processed. This control system includes a probe secured at the center of a rear wall of a tumbling compartment having an interrupted current path therethrough arranged so that wet articles being tumbled occasionally will complete the interrupted current path and thereby condition the control system for terminating the drying. Although this method of dryness control is substantially accurate when a large load of articles is being processed, one of its major disadvantages is that when a small load of articles is being processed the articles may not contact the probe with sufficient frequency for the system to accurately control the dryness of the articles.
In U.S. Pat. No. 3,809,924 there is described a system for controlling the drying process of articles which again is dependent upon the moisture content of the articles being dried. The invention described therein is based on the observation that completely dry articles which are moved in a tumbling dryer become electrostatically charged. Accordingly, the electrostatic charge occurring in the articles being processed is sensed and an electrical signal indicative of the field intensity of the electrostatic charge is used to control the drying operation. A disadvantage of this system is that it lacks the ability to control a plurality of degrees of dryness. An electrostatic charge would not occur on articles until they are substantially dry; accordingly, this system would not allow the user to only partially dry the articles. Where many dryness control systems are incapable of drying to a moisture content of zero (0) percent, this control system is incapable of drying to a moisture content of any value other than substantially zero (0) percent.
In U.S. Pat. No. 3,822,482 there is described a system for controlling the drying process of articles which again is dependent upon the moisture content of the articles. In the invention described therein two conductive electrodes are bridged by the moisture laden articles as they are tumbled in a compartment. As in the case of U.S. Pat. No. 3,333,345, a disadvantage of this system is its inability to accurately control the dryness of a small number of articles. Furthermore, by utilizing the moisture content of articles to determine their dryness the control system is limited to dryness sensing unless additional sensors and associated circuitry are incorporated thereby adding to the cost of the control system.
The means and method for controlling the operation of a drying apparatus described hereinafter overcome the disadvantages of the prior art control systems described above by sensing the temperature of the air being used to dry the articles as it enters the compartment and the temperature of the same air as it leaves the compartment and deriving, as a function of the maximum difference between such temperatures and a preselected dryness level, a final temperature difference which is indicative of the selected dryness level. Since temperatures are being sensed to control the dryness operation of the apparatus the same means can be utilized to inexpensively control other operation variables of the apparatus such as the temperature of the air used for drying, the temperature of the air within the compartment after the desired level of dryness has been achieved in order to avoid setting wrinkles, and an excessively high compartment temperature indicative of a loaded or clogged lint filter.